1. Field of the Invention
The present invention relates to curable compositions comprising blends of curable active hydrogen-containing polymers and curing agents therefor.
2. Brief Description of the Prior Art
Color-plus-clear coating systems involve the application of a colored or pigmented basecoat to a substrate followed by the application of a transparent or clear topcoat to the basecoat and are becoming increasingly popular as original finishes for automobiles. The color-plus-clear systems have outstanding gloss and distinctness of image and the clear coat is particularly important for these properties.
A serious problem associated with automotive finishes is acid etching which is the tendency of acidic materials to permanently spot and actually etch away the coating when placed in direct contact with the coating. Because many portions of the world, particularly industrial areas, have acidic environments, rain water becomes acidic and when left on the painted surface of an automobile, will cause this etching. If serious enough, the automobile may have to be repainted since it is very difficult to polish and buff out the spotting due to the acid etching. Therefore, it would be desirable to develop a curable composition which could be formulated into a clear coating composition which would have resistance to acid etching while maintaining the desired properties associated with clear coats for automobiles such as gloss, distinctness of image and exterior durability.
U.S. Pat. No. 4,818,796 discloses a clear coating composition which does have resistance to acid etching. The clear coating composition comprises as the resinous film-forming material a hydroxyl-containing polymer and a curing agent such as an aminoplast resin or a blocked isocyanate curing agent. The hydroxyl-containing polymer is prepared from a mixture of monomers comprising a monomer represented by the formula: ##STR3## where R stands for tertiary aliphatic hydrocarbon group having 4 to 26 carbon atoms; a polymerizable alpha, beta-ethylenically unsaturated carboxylic acid and optionally at least one other polymerizable alpha, beta-ethylenically unsaturated monomer. Although the curable compositions when formulated into a clear coating composition have outstanding resistance to acid etching along with good gloss and distinctness of image, the compositions unfortunately have poor exterior durability, having a tendency to crack when exposed for long periods outdoors, particularly hot humid atmospheres associated with the state of Florida, U.S.A.